The present invention relates to a multi-channel biological signal telemetry system for measuring or monitoring biological signals, such as electroencephalograms, which are led from a human scalp or the surface of the cerebral cortex as feeble potential variations (of several to hundreds of μV) having frequency components superposed thereon, an electrocardiogram, an electromyogram, respiratory waveforms, SpO2, or the like.
Since the physical and/or mental state of a person can be determined by frequencies of electroencephalograms obtained by the person, a system for controlling equipment, such as a reclining apparatus, by utilization of electroencephalograms has hitherto been developed. For instance, Japanese Patent Publication No. 8-71050A discloses a system capable of creating a comfortable environment by controlling an equipment on the basis of not only information about electroencephalograms sampled at the present time, but also the difference between the preset desired physical and/or mental state and the present physical and/or mental state. This system is configured such that a detected electroencephalogram is transmitted in a wireless manner, and frequencies and intensities of the received electroencephalogram is analyzed to evaluate comfortableness of the environment.
Because human electroencephalograms are very feeble electrical signals and include random waveforms called brain noise, difficulty is encountered in determining an S/N ratio and sampling electroencephalogram data. For this reason, Japanese Patent Publication No. 10-262943A teaches that: electroencephalogram data sets are detected from a plurality of points on a surface of a scalp; prescribed frequency components are extracted respectively from the thus-detected plurality of sets of electroencephalogram data; frequency band differential data pertaining to respective frequency ranges is determined after having applied common temporal weighting to the prescribed frequency components data sets; and an electroencephalogram (EEG) topography map is displayed on the basis of the frequency band differential data.
More specifically, under the electroencephalogram measurement method disclosed in this publication, an apparatus is configured such that electroencephalogram data of respective channels detected by cap-shaped electrodes are amplified by a multi-channel amplifier and converted into digital data by an A/D converter; prescribed frequency components are extracted from the thus-converted digital data in a digital band pass filter section; data of respective channels are subjected to common temporal weighting in a window function section; the thus-temporal-weighted data are converted into data in a frequency range by a frequency analysis processing section; a frequency band differential operation section determines frequency band differential data for each data frequency range of each channel; and an indicator displays an EEG topography map based on mapping data formed from the frequency band differential data.
Furthermore, Japanese Patent No. 2827969 discloses a medical telemetry system of digital modulation scheme and a medical telemetry apparatus. Particularly, the medical telemetry apparatus does not have any biological signal measurement section, but receives biological signal data detected and digitized by another piece of medical equipment by way of a dedicated line, and transmits the thus-received data in a wireless manner.
This medical telemetry system comprises: i) a bedside monitor which measures biological signals of a patient and outputs measurement data resulting from digitization of the thus-measured data; ii) a medical telemetry apparatus which includes frequency setting means for modifying and setting a transmission frequency; receives the measured data by way of a dedicated line; adds to the thus-received data a sender identification code, which is to become a radio channel code indicating a transmission frequency set by the frequency setting means, to thus acquire transmission data; and sends a modulated wave resulting from digital modulation of a carrier wave having a transmission frequency set by the transmission data through radio transmission; and iii) a central monitor which receives the modulated wave; demodulates the received modulated data to thereby obtain the transmission data; compares a receiver identification code with the sender identification code in the transmission data; and displays and records measurement data in the transmission data only when these identification codes coincide with each other.
Further, Japanese Patent No. 3125077 discloses a portable telemetry apparatus capable of preventing consumption of a battery in the event of abnormal placement of electrodes. The biological signal telemetry apparatus is configured so as to be carried by a patient; is supplied with a direct current power source from a built-in battery; and transmits biological signal waveforms led by the electrodes placed on the subject, by a radio signal from a transmission circuit. This biological signal telemetry apparatus comprises an electrode anomaly detection circuit which detects the state of the electrodes placed on the subject and outputs an electrode detachment signal for a period during which the electrodes are placed anomaly; and a switch circuit which interrupts supply of the direct current power source to the transmission circuit during a period in which the switch circuit is receiving the electrode detachment signal from the electrode anomaly detection circuit.
A conventional electroencephalogram telemetry apparatus, or the like, employs a medical telemetry band of 400 MHz, at which a data transmission speed is quite low. Accordingly, great difficulty is encountered in transmitting electroencephalogram data, which require high resolution and high sampling per channel, on 32 channels or more.
Further, a general transceiver consumes a considerable amount of current, regardless of an operating state, only when the power of the transceiver is active. Therefore, the current consumed by the transceiver (i.e., consumption of a battery) becomes dominant over the current consumed by an amplifier circuit (consumption of the battery).
Further, the greater the number of, e.g., amplifier circuits, are additionally provided to implement multi-channeling during transmission of electroencephalogram data, the greater the consumed current increases. Therefore, in an attempt to embody a portable multi-channel telemetry apparatus which is operated by utilization of a battery as a power source, an operable time becomes fairly shorter. For instance, long-term operation of 24 hours or longer is highly difficult.
As described above, a system configuration of a related-art electroencephalogram telemetry apparatus has failed to implement a portable multi-channel electroencephalogram telemetry system of 32 channels or more capable of performing battery-powered operation for 24 hours or longer.